Telephone system



Q May 12, 1931. J. H. voss ET AL TELEPHONE SYSTEM Filed u y 5. 1929 3 Sheets-Sheet 1 FROM .B UV/(S Iru.rsu nrs Jo Z'Ln HlJ'oss Thmnas F Brasher mm Fm L. BAN/(5.

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y 1931- I J. H. voss ETAL l$04,575

TELEPHONE SYSTEM Filed July 5, 1929 3 Sheets-Sheet 2 'HOXQ HJNVAIH 0.1.

m mvw 01 Jul-m H.Uuss Thomas F Cracker May 12, 1931. J. H. Voss ET AL TELEPHONE SYSTEM Filed y 5 1929 S Sheets-Sheet 3 ImrenTurs- John H U055 Thomas E Ern'cksr' ame 7' recs earaar JOE-IN VGSS, 6F BERWYN, AND THOMAS F. GRGCKER, OF CHICAGO, ILLINOIS, AS-

SIGNORS T RESERVE HQLDING COMPANY, 035 CHICAGO, ILLINOIS, A CORPORATION or DELAVIARE Application filed July 5,

This invention relates to telephone systems in general but is concerned. more particularly with small systems of the'type commonly known as private branch exchanges and with the method of inter-connecting such systems with public telephone systems. p

A private branchexchange hereinafter designated P. is a relatively small but complete telephone system designed priw marily for furnishing local telephone service between various telephones in a business establishment orother organization. Such exchanges are, in fact, branches of a public telephone system and are connected with the public system by one or more trunks as required by traflic conditions.

A private branch exchange may be of the manual or automatic type or it may be a combination'of the two. In the latter type of exchange local calls are completcd'automatically by the branch exchange subscribers while all incoming calls from the public telephone system are intercepted and completed by an attendant. This arrangement is desirable since it is not usually practicable to list the local telephone number of each branch. exchange subscriber in the public telephone directory.

A modified system has been proposed in which the P. B. X. switching apparatus is to be installed in an exchangeof the public telephone system and separate lines extended to each P. B. X. telephone. This arrangement results in a considerable saving in auxiliary equipment such as storage batteries ringing machines, etc. The system has not been entirely satisfactory, particularly when the P. B. X. is of the attended type as the additional line plant required Offsets the saving in auxiliary equipment. The main object of this invention is the provision of an improved system of the above general type in which the obj ectional features inherent in previous systems are eliminated and which is adapted for commercial use.

In centralized switching systems of the type described there are often several business concerns between which there is c0nsiderable telephone traffic. Special trunking facilities between the two private exchanges "IEIJEPI-IONE SYSTEM 1929. Serial No. 376,215.

may be provided so that calls between these exchanges will not tie up equipment of the public exchange. The inter-exchange service may be full automatic or it may be hanlled on the same basis as incoming calls from the public exchange. It is with the latter type of service that this invention is concerned, one of the feat ures being an arrangement whereby the same trunks are used for incoming calls from either the public exchange or from another private exchange. It will be understood that these trunks may also be made accessible to selectors of the public exchange if service conditions make such an arrangement desirable.

'ther features of the invention relate to improved circuits and apparatus for providing more eiiicient and economical service in systems of the type described.

The foregoing features together withothers not specifically mentioned will be explained in detail hereinafter. with reference to the drawings comprising Fi e. 1, 2, 3, and l .These drawings show by means of the usual circuit diagrams a suiiicient amount of the equipment in a telephone system embodying the invention to permitthe invention to be readily explained and understood. The drawings should be arranged Vertically in numerical order with Fig. 1 at the top and with corr spending lines in alignment. The apparatus shown in Fig. 1 and Fig. 2 is assumed to be located in a public automatic exchange and that in Fig. 3 located on the premises of a P. B. X. subscriber. Fig. l is a schematic diagram showing the trunking between a main exchange and a branch exchange embodying the features of the invention. 7

Referring now to Fig. 1, CO is an incoming connector in which terminates two trunks, one accessible by wayof the local and toll connectors of the public exchange, the other accessible by way of selectors in either the public exchangeor another private exchange. A trunk from the connector also extends to the attendants position, and by way of its bank wipers and banks, the connector has access to the various lines of the P. X. Mechanically, connector 00 is maticsuhsta similar to the connector shown in United States Patent No. 1,580,490 to Jacobson. The circuits of the switch which relate solely to its function as a connector, that is, the-ver erator G, ringing interrupter I, and busy tone generator BT which are common to all switches, such as connector CC of the P. B. X. In practice, separate auxiliary equipment would not be provided for each P. B. X. but similar equipment of the public exchange would be used in commonl Referring to Fig. 2, LS and LS represent lineswitches terminating respectively .a P. B. X. line and a line from the attendants position. hese switches are of the well known rotary type having no normal or home position. Connector LC, shown in skeleton form, may be of the well known type commonly known as a P. A. X. connector such as that shown in U. S. Patent No. 1,582,226 to The connector is accessible to lineswitches of the P. B. X. and has access to these lines and to trunks both to the public exchange and to one or more other private exchanges. The connector switches over and functions as a selector when one of the outgoing trunk levels iscalled.

In Fig. 3 is shown two ordinary autoions T and T1 terminating in P. B. X. ines. Substation T is associated with lineswitch LS (Fig. 2) and substation T1 is associated with a similar lineswitch which is not shown. The attendants telephone set AS includes the usual transmitter TB, receiver REC, calling device or dial CD, and is equipped with a key K for, answering 'and' extending calls over the extension line connector such as connector LC. The banks of incoming selectors and local selectorsare mult plied. These selectors have access to the various main exchange connector groups including a group of rotary connectors of which connector CM is one. The rotary connectors have access to the branch exchange line groups of which one trunk terminating in branch exchange connector CC is shown. Connectors CC and LC, lineswitches LS and LS1, operators set AS, trunk relay group TR-G and substations T and T1 are shown in detail in Figs. 1-3. It will be noted that a trunk from the banks of selector SM is shown extending to connector CC. This trunk may also be accessible to incoming selectors or switching connectors of other branch exchanges as will be explained in later paragraphs Connector CC and the associated trunk circuits are adapted to operate when called from either a connector or a'selector. A call from an outside subscriber is extended to the connector which signals the attendant over the simplex control trunk. The attendant determines the name of the party wanted and then dials back over the trunk to set the wipers of the connector on the contacts to the. proper P. B. X. line. The connector is then. arranged to give the usual answering supervision to the calling subscriber as soon as the attendant answers. After extending the call the attendant disconnects the control trunk from the telephone set and the trunk relays operate to provide answering and disconnect supervision. In case the P. B. X. line called is busy, the attendant can release the connection and set up the call to another line while the calling subscriber waits. Both the connector and the attendants set are arranged so that the dialling impulses cannot be heard.

The operation of the apparatus on toll calls is the same as on local calls except that the attendant is not signalled until the toll.oporator rings. The called line is signalled automatically, however, as in a local con nection.

The attendants position is also provided with a line over which local calls in the P. B. X. may be extended and received. The attendant as well as the P. B. X. subscribers can call public exchange subscribers and other inter-connected private exchanges by way of the local switching connectors and outgoing trunks. Local calls in the P. B. X. are completed under control of a calling subscriber and donot'involve any of the public exchange 7 apparatus.

Having briefly described the operation and the apparatus involved, a detailed description will now be given. A local call from a public exchange subscriber to a'P. B. X. line, 7

its operating circuit and transmits corresponding impulses to the vertical and rotary stepping magnets of the connector. The stepping circuits, as previously.mentioned, are similar to those shown in the above-referred to Jacobson patents, and will not be described in detail. It may be pointed out, however, that relays 110 and 11 1 which operate during the vertical and rotary stepping operations, respectively, short circuit a winding of repeating coil R at contacts 155 and 167 so that the calling subscriber does not hear the impulses from the calling device. lVipers 186188 are set on the contacts oi": the called line in response to the dialling of two digits and the connector tests the line in the usual way. If the called line is busy relay 113 operates'itrom ground on the test contact and locks up to ground at contacts 151. Busy tone is connected to the lower talking conductor at contacts 166 and is audible both to the callingsubscriber and to the attendant. The calling subscriber may hang up or may request the attendant to establish a connection with another extension line. The attendant then momentarily operates key K1 to the let-t, opening the simplex trunk circuit, and relay 108 releases. The circuit of relay 109 is opened and that relay releases and closes the circuit of the release magnet. Relay 109 also opens the direct current bridge across the incoming trunk conductors which permits the back-bridge relay of the calling connector to restore but has no further effect on the call at the time. Release magnet 118 operates and the wipers of the .connector restore to normal. Busy relay'113 also releases following the release of relay 109 and connector CC is placed in condition for reoperation. The attendant again actuates key K1 to the right and sets up another connection exactly as in the previous instance. If the called line is idle, relay 115 of the connector operates in series with the line relay of the called line and ringing current is sent over the calling line in the-usual manner. restore key K1 to normal, thus making the telephone set available for other calls and reconnecting the trunks to relay group TRG. It wil be recalled that relay 307 operated over itsupper winding when key 151 was operated to the right and that reli y 306 was also operated. As key K1 is restored to normal, contacts 319 close before contacts 318 open and leg 322 of the simplex trunk is extended by way of contacts 342, lower winding of relay 307, relay 308 to ground. Relay 108 of the connector 1) and relay 307 remain energized over this circuit and relay 308 also operates. Lamp L1 lights and remains lit until the called subscriber answers. When the called subscriber lifts the receiver the usual direct cur-rent bridge across the line. is closed and ring-cutoff re- The attendant will then lay 112 operates in the usual manner to stop the ringing and extend the called line loop to battery feed relay 107. Belay 107 operates over the called subscribers group and at contacts 1&7 and 1 18 disconnects the upper winding of relay 108 from the simplex trunk and connects the two windings of the relay in series to the trunk. The lower winding of relay 108 has a relatively high resistance and relay 308 of trunk relay group TRG (Fig. 3) is adjusted so that it will release under these conditions. Relays 108 and 307, how-. ever, remain operated. Relay 308 opens the circuit of lamp L1 at contacts 339 and lamp L1 is extinguished to inform the attendant that the call has been answered. Then the called subscriber hangs up, relay 107 will restore and again connect the upper winding alone of relay 108 in the previously described supervisory circuit. Relay 308 will again energize and close the circuit of lamp L1 which relights to inform the attendant that the call has been finished. Should the lamp continue to burn'the attendant will again reestablish a talking connection with the calling subscribed by operating key K1 to the right. The attendant may release the connection with the extension line and set up a new connection in exactly the same manner as described for the operation after a call to a busy line. In case both calling and called subscribers hang up, the connection is released without any action on the attendants part. The calling subscriber opens the circuit of relay 102 which deenergizes and opens the circuit of relay 104. Relay 1041 releases, and opens a point in the simplex operating circuit to permit relay'108 to release. Re lays 109, 112, and 115 then release and release magnet 118 operates to restore the wipers of the connector to normal position in the usual manner. At the attendants end of the trunk relays 306, 307 and 308 release and the apparatus is immediately in condition to receive another call.

The operation of the trunk apparatus on toll calls is exactly the same as the opera tion described for local calls except that the calling toll connector does not send out ringing current automatically when the called trunk is seized. Relay 101 consequently does not operate until such time as the toll operator causes the connector to ring. The incoming trunk from the selector level, however, is made busy immediately when the trunk is seized and the toll operator may hold up the connection without signalling the attendant as long as desired. WVhen the connector sends out ringing current, relay 101 operates, signals the attendant in the previously describedmanner and the connection to'the P. 'B. X. line is set up as previously described.

'The previously described call was extended by connectors in the public exchange. A call from a selector or switching connector level of either the public exchange or another P. B. X- will now be considered. The calling selector or switching connector having been operated to the proper level automatically selects a trunk to the P. B. X., for example the trunk comprising conductors 2l, terminating in connector CC. Ground is extended over release trunk conductor a to slowaelease relay 103 by way of contacts 122 and 133. Relay 103 operates, closes the line conductors through to line relay 106 at contacts 131 and 132, closes a circuit for slowto-operate relay 104 at contacts 130, and at contacts 133 connects ground to the simplex trunk as in the previous connection. Belay 106 operates, closes a point in the holding circuit of relay 104, at contacts 1 1-3 disconnects release trunk conductor 4 from the relay 102 at contacts 196 and at contacts 195 connects a busying ground to that conductor. The attendant is signalled and answers the call as described in the previous connection. Relays 103 and 109 operate as previously described, as does relay 105. Relay 105 by means of the usual contact arrangement reverses the direction oi current flow over the incoming trunk conductors for the purpose 0'5 supervising and metering the call. The attendant sets up the connector and the call is completed in exactly the same manner as described for connector level calls.

Local calls within the P. B. X. are completed automatically as was previously mentioned. F or example, the subscriber at substation T may call the subscriber at substation .Tl by way of lineswitch LS and connector LC. On lifting the receiver at substation T- a circuit is closed for line relay 202 01": lineswitch LS and that relay operates in the usual way to complete the testing circuit of the lineswitch. The lineswitch operates in the Well known manner and selects an idle trunk, for example, the trunk comprising conductors 216218, terminating in connector LG. The calling subscriber then dials the digits of the called line number and connector LG is operated into engagement with contacts of the called line. The connector tests and signals the called line in,

the usual manner and when the call is finished releases lineswitch LS and restores its own wipers to normal in the usual manner.

Should the subscriber at'substation T desire to call the attendant, connector LO will be operated to the contacts associated with the line assigned to the attendant, for example the line terminating in lineswitch LS1. Cut-0d relay 201 operates in the usual manner to disconnect relay 202 and ground from the talking conductors of the line comprising conductors 391 and 392. The connector rings out on the line in the usual manner to operate the bells B which are bridged across the line conductors in series with condenser 351. The attendant answers the call by operating key K to the right, thereby extending the'line conductors to the attendants tele phone set at contacts 311 and 313, disconnecting the bells and condenser from the line, and closing a circuit for relay 302 which may be traced from ground, contacts 314, and 325, upper winding of relay 302 to battery. Relay 302 operates and closes a circuit for relay 301 at contacts 327. Relay 301 operates, closes a locking circuit for itself at con tacts 324, opens the circuit of relay 302 at contacts 325, and closes a circuit for relay 303 at contacts 323. Relay 301 also closes a direct current bridgeacross the incoming line conductors at contacts 326, the bridge including the secondary winding of induction coil IC and contacts 332. The ringcut-ofi' relay of the connector operates over this bridge in the usual way to stop the ringin Relay 302 remains energized a short time after its circuit is openedat contacts 325 due to its slow releasing characteristics and maintains the attendants receiver circuit open at contact 329 so that ringing current will not affect the receiver. Relay 302 then deenergizes to close the receiver circuit and the attendant may conversewith the calling subscriber. The operation of relay 303 substitutes the bridge including the impulse contacts of the dial for the first mentioned direct current bridge, but this operation has no utility in this connection. When the calling subscriber hangs up the receiver-lineswitch LS and connector LC release in the usual manner. The attendant then restores key K to normal.

The subscriber at substation T may also call subscribers inthe public exchange or in another l. B. X. by operating connector L0 to a trunk level on which level the connector functions as a selector. For example, by. operating the connector to the tenth level the trunks, such as the one comprising conductors 22 F226 may be seized. These trunks terminate in incoming selectors such as selector ISM in the public exchange through which access may be had to any of the public exchange subscribers lines. The ninth level, for example, may be equipped with trunks extending to another P. B. X., such as the trunk comprising conductors 221223, which may terminate in either a selector or a connector in the branch exchange. The latter trunk may also to 'minate in a connector, such as connector CC in another private exchange, which will extend the call to an attendant for completion.

The attendant may also extend calls to the various P. B. X. lines or to the public exchange or to another private exchange in exactlythe sane manner as a P. B. X. calling subscriber. To extend a cal key K is operated to the right, whereupon relays 302, 301, and 303 operate as in the previous C011: nection, and close a loop for relay 202 of lineswitch LS1, which may be traced from ground, contacts 209, conductor 2391, contacts 818 and 326, secondary winding of induction coil IC, cont cts impulse contacts .335, contacts 331, and 311, conductor 392,,contact-s 20 i, wlnding of relay 202 to battery. Relay 202 operates, closes the usual testing circuit at contacts 210 and 211, whereupon lineswitch LS1 operates in the usual manner to selectan idle trunk, such as the trunk comprising conductors 2l62l8, terminating in connector LC. The operation of calling device CD interrupts the calling loop at impulse contacts and con-e nector LC is operated in the same manner as previously described. Relay 302 operates when the calling device is turned oil-normal, as in the previous connection and opens the receiver circuit at con tcts 329. The connection is released by restoring key K to normal, thereby opening the loop circuit to lineswitch S1 and connector LC at contacts 311 and 313. Should-key K be operated while the attendants set is connected with an incoming trunk by way of key 'K1, the simplex control trunk willnot be opened due to the holding circuit closed atcontacts 312. This permits the attendant to extend acon nection over conductors 39l'and 392 and lineswitch LS1 while holding up a connection from a public exchange by way of the simplex trunk. The operations under these conditions are exactly the same as those described in previous connections.

Having described the invention, what is thought new and is desired. to have protected by Letters Patent will be pointed out in the appended claims.

IVha-t is claimed is 1. In a telephone system comprising a main exchange and a branch exchange, switching apparatus at the main exchange for completing connections between main exchange subscribers and branch exchange subscribers, other switching apparatus at the mainexchange for completing connections between branch exchange subscribers, a branch exchange attendants position located at a. point remote from thermain exchange, a main exchange trunk terminating in said first switching apparatus, and a branch of said trunk extending from said first switching apparatus to said position.

2-. In a telephone system comprising a main exchange and a branch exchange, switching apparatus at the main exchange for completing connections with branch exchange subscribers, a branch exchange attendants position located at a point remote from the main exchange, a trunk extending from the main exchange to said switching apparatus, said trunk having a branch ex tending to said position, and means responsive'to a call over said trunk for signalling the attendant over said branch.

m in exchange and a branch exchange.

switching apparatus in the main exchange for completing all local calls within the branch exchange, other switching apparatus in the main exchange for completing calls incoming to the branch exchange from the main exchange, a branch exchange attendants position remote from the main exchange, subscribers lines terminating in said fi st switching apparatus, atrunk extending from the main exchangeto said switching apparatus, a branch of said other trunk extending to said position, means responsive to a call over said trunk for extending the call' to said position via said branch, and means controlled by the attendant over said branch for directively operating said other switchin apparatus to further extend the call to I called line.

5. In a telephone system, a calling line, switching apparatus accessible to'said line, a connector switch, a trunk terminating in said switch and accessible to said switching apparatus, an attendantsposition, a second trunk terminating in said switch and extending to said position, means controlled by the calling subscriber for directively operating said switching apparatus to extend a call to said switch via said first trunk, and means responsive to the extension of the call for rendering said switch directively controllable by the attendant over said second trunk.

6. In a telephone system, arcalling line, switching apparatus accessible to said line, a connector switch, a trunk terminating in said switch and accessible to said switching apparatus, an attendantsposition, a second trunk terminating in said switch and extending to said position, means controlled by the calling subscriber for directively operating said switching apparatus to extend a call to said switch via said first trunk, means responsive to the extension of the call for signalling the attendant over saidsecond trunk, and means controlled by the attendantover said second trunk for directively operating said switch to further extend the call.

7. In a private branch automatic telephone system in which the switching apparatus is located at a point remote from the subscribers premises, an attendants position located at the subscribers premises, a trunk connecting the switching apparatus and said position, means for extending an incoming call to said position via said trunk without directly operating said switching apparatus, and means controlled by the attendant over said trunk for directively operating the switching apparatus to further extend the call.

8. In a telephone system, a directively controlled switching device, two trunks terminating in said device, a battery, and means responsive to the seizure of said device over one of said trunks for successively connecting the two poles of said battery to the other of said trunks.

9. In a telephone system, a connector switch, an incoming trunk and a control trunk each comprising a plurality of conductors terminating in said switch, means for extending a connection to said switch over'two conductors of said incoming trunk in series, and means responsive to the extension of said connection for connecting a characteristic potential to two conductors of said control trunk in parallel.

10. In a telephone system, a connector switch, an incoming trunkand a control trunk each comprising a plurality of conductors terminating in said switch, means for extending a connection to said switch over two conductors of said incoming trunk in series, a battery, and means responsive to the extension of said connection for successively connecting the two poles of said battery to two conductors of said control trunk in parallel.

11. In a telephone system, an automatic switch, an attendants position, two trunks terminating in said switch, means responsive to a call for seizing said switch over one of said trunks, means responsive to the seizure of the switch for signalling the attendant over the other of said trunks, means in the switch responsive to the attendants answering the call for reversing the direction 01": cur rent flow over said first trunk, and means controlled by the attendant over said other trunk for directively operating said switch to extend the call.

12. In a telephone system, an automatic switch, an attendants position, twotrunks terminating in said switch, means responsive to a call for seizing said switch over one of said trunks, means responsive to the seizure of the switch for extending the call to said attendant via the other of said trunks, means in the switch responsive to the attendants answering the call for reversing the direction of current flow over the first of said trunks, means controlled by the attendant over the other of said trunks for dircctively operating said switch to further extend the call to a called subscriber, and means responsive to the called-subscriber answering the call for increasing the resistance of said other trunk. I

13. In a telephone system, an automatic switch accessible over two paths, a control trunk terminating in said switch, a source of current, means in the switch responsive to itsseizure over one path for connecting said current source to said trunk, and means in the switch effective when the connector is seized over the other path and responsive to alternating current transmitted thereover for connecting said current source to said trunk.

14. In a telephone system, an automatic switch accessible over two paths, a control trunk terminating in said switch, means in the switch responsive to its seizure. over one path for rendering said switch directively operable over said trunk, and means in said switch effective when the switch is seized over the other path and responsive to alternating current transmitted thereover for rendering said switch directively operable over said trunk. I

15. in an automatic switch accessible over two paths, a relay, means responsive to the seizure of the switch over one path for operating said relay, and means responsive to the seizure of the switch over the other path for rendering said relay operable responsive to alternating current received over said other path.

16. in a telephone system, a switching device, a battery teed relay in said device, two trunks terminating in said device,,n1eans for extending a call to said device over either of said trunks, means in said device responsive to the extension of a call over one of said trunks for bridging said relay across the conductors of said trunk, and means responsive to the extension of a call over the other of said trunks for disabling said relay.

17. In a telephone system comprising a private branch exchange and a public exchange in which the local and incoming switching apparatus of the private exchange is located at the public exchange, subscribers stations and an attendants switchboard located at the private exchange suhscribers premises, lines connecting the stations with the local switching apparatus, and a control trunk connecting the switchboard with said incoming switching apparatus.

18. In an automatic telephone system com prising a public exchange and a private branch exchange, switching apparatus at the public exchange for completing local connections between branch exchange subscribers,

other'switching apparatus at the public ex change for completin calls from public exchange subscribers and branch exchange subscribers, substations and an attendants switchboard at the branch exchange subscribers premises, lines connecting the substations with said first switching apparatus, and trunk lines connecting the switchboard with said other switching apparatus.

In witness whereof, I hereunto subscribe my name this first day of July, A. I). 1929. JOHN'H. VOSS. In witness whereof, I hereunto subscribe my name this first day of July, A. D. 1929.

THOMAS F. CROCKER. 

